1. Field of the Invention
The present invention relates to optical detectors that convert light into an electric current, and more particularly to detectors used in high speed fiber optic communication.
2. Discussion of Related Art
As the data rates used in fiber optic communications go above 40 Gbits/second high speed, sensitive optical detectors are need. III-V semiconductor PIN detectors using materials such as GaAs and InGaAs have been used in this capacity. However, with the invention of the Lateral Trench Detector (LTD) (U.S. Pat. No. 6,177,289) it has become possible to achieve these high speeds using silicon PIN detectors A drawback of silicon PIN detectors, however, is it""s relatively large capacitance compared to the more conventional PIN detectors. This capacitance in turn requires the use of lower impedance amplifiers with an attendant increase in circuit noise that limits the sensitivity achievable using the silicon PIN detectors.
An avalanche detector operates similarly to a silicon PIN detector but uses avalanche multiplication to achieve gain (more than one electron per photon). Because of the improved,gain the detector is less sensitive to circuit noise. Further, receivers utilizing this technology can achieve higher sensitivities.
Therefore, a need exists for a method of fabricating LTDs that realize avalanche gain.
According to an embodiment of the present invention, a method of forming an avalanche trench optical detector device on a semiconductor substrate, comprising forming a first set and a second set of trenches in the substrate, wherein trenches of the first set are alternately disposed with respect to trenches of the second set, filling the trenches with a doped sacrificial material, and annealing the device to form a multiplication region in the substrate. The method comprises etching the doped sacrificial material from the first set of trenches, filling the first set of trenches with a doped material of a first conductivity, etching the doped sacrificial material from a second set of trenches, and filling the second set of trenches with a doped material of a second conductivity. The method further comprises providing separate wiring connections to the first set of trenches and the second set of trenches.
The first set and the second set of trenches in the substrate are formed simultaneously.
Etching the doped sacrificial material from the first set of trenches further comprises removing the doped sacrificial material from a surface of the device, and masking the second set of trenches.
Providing separate wiring connections further comprises exposing the doped material filling the first set of trenches and the doped material filling the second set of trenches to a surface of the device, and providing each of the first set of trenches with a first set of contacts and the second set of trenches with a second set of contacts.
Annealing further comprises depositing a diffusion barrier layer over a surface of the device prior to forming the multiplication region, and removing the diffusion barrier layer from a surface of the device after forming the multiplication region.
The material of the first conductivity comprises n type doped poly-silicon and the material of the second conductivity comprises p type doped poly-silicon. The material of the first conductivity comprises p type doped poly-silicon and the material of the second conductivity comprises n type doped poly-silicon.
The substrate includes a semiconductor material, a SiO2 layer deposited over the semiconductor material, and a SiN layer deposited over the a SiO2 layer.
Etching the sacrificial material from a second set of trenches further comprises the step of exposing the sacrificial material of the second set of trenches to a surface of the device by mechanical polish.
The doped sacrificial material is one of p type doped poly-silicon and n type doped poly-silicon.
According to an embodiment of the present invention, a method of forming an avalanche trench optical detector device on a semiconductor substrate, comprises forming a first set and a second set of trenches in the substrate, wherein trenches of the first set are alternately disposed with respect to trenches of the second set, filling the trenches with a doped sacrificial material, and forming a multiplication region in the substrate surrounding a bottom portion of the trenches. The method further comprises etching the doped sacrificial material from the first set of trenches, filling the first set of trenches with a doped material of a first conductivity, etching the doped sacrificial material from a second set of trenches, and filling the second set of trenches with a doped material of a second conductivity. The method comprises providing separate wiring connections to the first set of trenches and the second set of trenches.
The first set and the second set of trenches in the substrate are formed simultaneously.
Etching the doped sacrificial material from the first set of trenches further comprises removing the doped sacrificial material from a surface of the device, and masking the second set of trenches.
Providing separate wiring connections further comprises exposing the doped material filling the first set of trenches and the doped material filling the second set of trenches to a surface of the device, and providing each of the first set of trenches with a first set of contacts and the second set of trenches with a second set of contacts.
The material of the first conductivity comprises n type doped poly-silicon and the material of the second conductivity comprises p type doped poly-silicon. The material of the first conductivity comprises p type doped poly-silicon and the material of the second conductivity comprises n type doped poly-silicon.
The doped sacrificial material is one of p type doped poly-silicon and n type doped poly-silicon.
According to an embodiment of the present invention, an avalanche trench optical detector device comprises a substrate, a first set of trenches in the substrate having a doped material of a first conductivity, and a second set of trenches in the substrate having a doped material of a second conductivity, wherein trenches of the first set are alternately disposed with respect to trenches of the second set. The device comprises a multiplication region in the substrate surrounding a lower portion of the first set and the second set of trenches, wherein the multiplication region comprises about 10 percent of a photoactive area, and a first connection and a second connection coupled to the first set of trenches and the second set of trenches respectively.